SOLUTION: Marcus can drive his boat 36 miles down the river in 3 hours but it takes 4 hours to return upstream. Find the rate of the boat in still water and the rate of the current.
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Question 1152112: Marcus can drive his boat 36 miles down the river in 3 hours but it takes 4 hours to return upstream. Find the rate of the boat in still water and the rate of the current. Answer by ikleyn(52814) (Show Source):
Let u = the boat rate in still water, in mph,
let v = the rate of the current.
The equation for the effective rate downstream is
u + v = = 12 mph. (1)
The equation for the effective rate upstream is
u - v = = 9 mph. (2)
Thus you have the system of two equations in two unknowns (1) and (2).
To solve it, add the equations. You will get
2u = 12 + 9 = 21,
hence, u = 21/2 = 10.5 mph.
Then from equation (1), v = 12-10.5 = 1.5 mph.
ANSWER. The rate of the boat in still water is 10.5 mph.
The rate of the current is 1.5 mph.
Solved.
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It is a typical and standard Upstream and Downstream round trip word problem.
